It is well known in the manufacture of multi-layered products, such as resilient floor, wall, or ceiling coverings, or resilient desk, table, or counter tops, and the like, that it is often necessary to bond together two or more layers of dissimilar synthetic polymeric materials and that it is often difficult to obtain a strong and permanent bond between such dissimilar synthetic polymeric materials that will successfully resist delamination of the layers.
Such difficulties often are believed to arise in the bonding of such dissimilar synthetic polymeric materials because of differences in surface energies. For example, if atoms from two dissimilar synthetic polymeric materials cannot be close enough to each other, perhaps because of large dissimilarities or disparities in polarity, van der Waals forces cannot be adequately taken advantage of to create strong and permanent bonding that will resist delamination. Nor is it believed that hydrogen bonding can be adequately taken advantage of in such situations. Many proposals have been made heretofore to overcome such difficulties and to improve the bond between such dissimilar synthetic polymeric materials but none has been found to be completely satisfactory to date.
The present invention will be described with particular reference to the bonding of dissimilar synthetic polymeric materials, such as, for example, vinyl resin materials and polyurethane or acrylated polyurethane resin materials but it is to be appreciated that the principles of the present invention are equally applicable to other equivalent dissimilar synthetic polymeric materials. In the same way, the present invention will be described with particular reference to multi-layered decorative sheet materials such as resilient floor coverings, utilizing such dissimilar synthetic polymeric materials but, again, it is to be appreciated that the principles of the present invention are equally applicable to other multi-layered products utilizing such dissimilar synthetic polymeric materials or layers.
In the manufacture of resilient floor coverings, normally a base layer or substrate is laid out in a substantially flat, horizontal condition. Such a base layer or substrate is customarily a felted or matted fibrous sheet or overlapping, intertwined fibers and/or filaments, usually of asbestos or of natural or synthetic or man-made fibers of cellulosic origin, although many other forms of sheets, films, or textile materials and many other fibers and/or filaments may be used.
Upon this substantially flat, horizontal base layer or substrate is then applied a substantially uniform base layer of a liquid or semi-liquid resinous composition containing a synthetic polymeric material, usually an ungelled polyvinyl chloride plastisol, and usually containing a blowing or foaming agent. This liquid or semi-liquid plastisol composition is subsequently heated and gelled at an elevated temperature to a relatively firm condition.
This relatively firm, gelled polyvinyl chloride plastisol may then be printed with a decorative multi-colored pattern or design in which certain predetermined areas may contain a blowing or foaming inhibitor which subsequently modifies the action of the blowing or foaming agent in those certain predetermined areas.
A substantially uniform wear layer of a clear liquid or semi-liquid resinous composition, containing usually another polyvinyl chloride plastisol but normally not containing any blowing or foaming agent is then applied as a wear resistant top coating to the surface of the gelled, printed base layer of polyvinl chloride plastisol and is subsequently gelled and firmed thereon either as a separate operation or jointly in connection with a fusion and blowing or foaming operation of the base layer of polyvinyl chloride plastisol.
Thus far, there is relatively little or no difficulty in creating a strong and permanent bond or adhesion between the base layer of polyvinyl chloride plastisol and the wear layer which is also of polyvinyl chloride plastisol. Such layers just naturally bond together immediately upon contact, followed by the subsequent heating.
It is then frequently desired to provide a top surface coating on top of the surface of the polyvinyl chloride wear layer and such top surface coating is often desired to be a polyurethane or acrylated polyurethane resin coating because of their superior physical and chemical properties and characteristics. However, in many instances, it is found that the bond or adhesion between the vinyl resin material of the wear layer and the polyurethane or acrylated polyurethane resin material of the top surface layer is not as strong or as permanent, as desired, and does not resist delamination as well as desired. It is believed that such is due to the fact that the wear layer material and the top surface coating material are dissimilar synthetic polymeric materials.